1. Field of the Invention
The present invention relates to a pusher centrifuge with at least two screening drums which rotate in a housing and in which material for centrifugation is fed into the interior at one end, and with at least one pusher ring between two screening drums, which carries out an oscillating movement in the axial direction of the screening drums to advance the partially dewatered centrifugation material on the interior of the following screening drum, in each case in the direction of a solid material outlet.
2. Description of Background and Other Information
Such pusher centrifuges are known from U.S. Pat. Nos. 4,217,226 and 4,209,405, and Swiss Patent Nos. 624,858 and 627,376, and serve for the continuous dewatering of material for centrifugation, in which the material is delivered via a feed pipe to the inner end of a centrifugation chamber and is dewatered successively on the inside of the screening drums. During this operation, the material to be centrifuged is gradually advanced in the direction of a solid material outlet by the oscillating movement in the axial direction of one or more pusher rings between adjacent screening drums, and at the same time material for centrifugation which has not been dewatered is added in the vicinity of the pusher base.
Such a pusher centrifuge has several screening drums, each pair of adjacent screening drums oscillate relative to one another in the axial direction and the edge of the inner screening drum in each case acts as a pusher ring. For example, in a two-stage centrifuge it is the drum, in a three-stage centrifuge the pusher base and the second drum, and in a four-stage centrifuge it is the first and third drums which oscillate in the axial direction.
With such a pusher centrifuge, continuous dewatering of material for centrifugation is possible, the material being gradually dewatered in the centrifugal field in the course of the advance on the inside of the screening drums from the material inlet to the solid material outlet and reaching the solid material outlet in a largely dewatered state, while the filtrate is forced outwardly through the screening drums and is drawn off there.
Especially in the case of high centrifugation material throughputs and fine grains, with such pusher centrifuges, caked layers form on the screening drums and do not change significantly during the advance toward the discharge. The solid cake which is formed becomes increasingly more compact and thus less permeable, so that the degree of dewatering and the residual moisture of the discharged solid material in the case of specific materials for centrifugation is still not ideal and necessitates a lengthening of the dewatering time and a higher rotation speed and a high energy consumption.
It has already been proposed that the cake of solid material which is formed during the dewatering operation should be loosened by inclined surface elements on the pusher rings, thus accelerating the dewatering. In the case of many materials for centrifugation, this measure leads to an improvement in the moisture extraction without increasing the speed of rotation of the screening drums and the residence time of the material for centrifugation. However, in the case of particularly delicate materials for centrifugation, the abrupt shearing movement of such pusher centrifuges gives rise to the danger of grain breakage and abrasion.